1. Field of Invention
The present invention relates to separation of Luminance (Y) and Chrominance (C) in a TV composite signal, particularly to the design of an adaptive three-dimensional luminance/chrominance (Y/C) separation comb filter.
2. Description of Related Art
A typical color TV decoder receives composite TV signals as input. The color decoder subsequently separates Luminance (Y) and Chrominance (C) from the input signal by using a comb filter. The comb filter then applies band-pass filtering to the C signal and band-stop filtering to the Y signal. The C signal is then de-modulated back to the base-band region. A low-pass filter then band-limits both the de-modulated C signal and the Y signal. Finally, the band-limited Y and C signals are converted to Red, Green, and Blue outputs.
Composite signals allocate Y and C in three-dimensional spectral positions in a three-dimensional spectral space. When represented in a one-dimensional or a two-dimensional subspace of the three-dimensional spectral space, the spectrum of Y and C overlap each other. Therefore, only three-dimensional comb filters can separate Y and C from a digitized composite image sequence completely.
Currently, only a few high performance adaptive three-dimensional Y/C comb filters exist for digital color decoders. Moreover, if the type and location of each edge can be determined, the Y/C comb filter can separate the Y from the C clearly to improve the performance.
However, even the more sophisticated comb filter designs today lack a proper adaptive decision-making model.
Some comb filters employ an xe2x80x9cafter-searching-edge adaptive methodxe2x80x9d. This method first detects whether an edge exists on the current sample pixel, and operates a comb filter in the direction at which the edge lies. This method performs well for color edges, but poorly for colorless edges.
Alternatively, some comb filters employ an xe2x80x9cafter-searching-color adaptive methodxe2x80x9d. This method first extracts a color signal from a TV signal, and operates a comb filter in the direction of the color signal with minimum energy. This method performs well for colorless edges, but poorly for color edges.
Accordingly, an adaptive decision-making model that determines the type and location of each edge for comb filters is needed.